{Anon for obvious reasons}
Yes. But possibly not in the way you were thinking of.
Waayyy back when I was still very much a green-horn / fledgling I was in charge of a revenue processing department that consisted of a whole bunch of AS400 batch queries (CSV output of course) that was imported in to Excel using various macros which also had various macros and look-up tables that processed and presented the data in an easy for users to edit format. Once they were done updating their figures all they had to do was hit a button that then exported that unholy mess in to a MS-Access DB (shudders... yeah, I know).
Anyway - For {$reason} I decided to write some code (functions were distributed between a mixture of VB, VBA and a few batch files) that would look for any numeric field and multiply the value by a very small random amount. It was very basic but used the day of the week to decide on how many fields to look for/update (Monday = 1 field, Tuesday = 2 different fields etc). Sometimes the random multiplication rounded the field value up, other times downwards, some times it made no difference. (And yes, I grew up on a diet of 80's movies about hackers and was heavily inspired by them. Side note - Office Space is a good one to watch).
Because the changes were so small and so random it wasn't picked up until their annual financial audit. By that stage the back-ups were useless.
Do I feel guilty? Yes. Would I do something like that ever again? I hope not. But Anon for obvious reasons.